The selective control of unwanted vegetation, such as, for example, weeds, is a major industry. Vegetation can be controlled using herbicides that are non-selective or selective, and systemic or contact. Non-selective herbicides kill or damage all plants to which they are applied, i.e., both desired and undesired vegetation. In contrast, selective herbicides eliminate or inhibit the growth of unwanted vegetation, while leaving the desired vegetation relatively unharmed. Contact herbicides are applied to the top growth, or portion(s) of the plant located above the soil surface. In contrast, systemic herbicides are initially taken up by the roots and/or the foliage of the plant and subsequently translocated to tissues that are remotely located from the point of application.
At present, there are several common types of selective herbicides on the market. The Phenoxy Acid-Type selective herbicides include 2,4-D (2,4-Dicholorophenoxyacetic acid), 2,4-DP (2,4-Dicholorophenoxypropionic acid, or Dichlorprop), and mecoprop (2-(2-methyl-4-chlorophenoxy) propionic acid). These systemic selective herbicides are initially taken up by the leaves, stem or roots of a plant, and subsequently moved throughout the plant. 2,4-D and 2,4-DP stimulate nucleic acid and protein synthesis and affect enzyme activity, respiration, and cell division, while mecoprop affects enzyme activity and plant growth. The Benzoic Acid-Type selective herbicides include dicamba, another systemic selective herbicide that is initially taken up by the leaves and roots of a plant and subsequently moved throughout the plant. Benzoic Acid-Type selective herbicides are similar to the Phenoxy Acid-Type selective herbicides described above.
Currently, these selective herbicides present major toxicological and environmental concerns. Attempts have been made to create selective herbicides that are effective, yet environmentally safe. Sedun et al. (U.S. Pat. No. 6,972,273) teach of a new class of environmentally safe selective herbicides that includes a transition metal component (Fe, Cu, Zn and/or Mn) and a chelating agent (aminopolycarboxylate, salicylate and/or amino acid). These metal complexones can be applied over an area of established grass and turf in which broadleaf weeds are growing and selectively remove these weeds, leaving the grass unharmed. Smiley (U.S. Pat. No. 6,323,153) teaches using various salts of chelating agents that are capable of forming stable coordination complexes with calcium and magnesium salts to control the growth of various weeds in lawns. Simpson (U.S. Pat. No. 6,258,750) teaches an algaecide, herbicidal and/or fungicidal composition including a metal, the chelating agent, ethylene diamine disuccinic acid (EDDS) or a salt thereof, and a source of calcium and chloride ions. Hudetz (U.S. Pat. No. 6,271,177) teaches a herbicide that combines a sulfonyl urea compound and a water-soluble iron compound, while Sedun (WO 01/50862) discloses a herbicidal composition containing a combination of maleic hydrazide (MH) and carboxylic acids. Each of the above-identified publications describing environmentally safe herbicides is hereby incorporated in its entirety by reference thereto.
While such environmentally safe selective herbicidal compositions have been shown to be effective, such compositions have to be applied at higher concentrations compared to conventional selective herbicides. Thus, there is presently a need for environmentally safe compositions that address one or more of the above-identified problems whilst providing effective control of lawn weeds without harming the lawn grasses.